The present invention relates to a method of forming a resist pattern in a step of a process of manufacturing a semiconductor device, and more specifically to a method of determining the thickness of a resist film and the structure and thickness of a film underlying the resist film, which can be applied to, for example, a photolithographic step.
Conventionally, in a step during the manufacture of a semiconductor device, a photoresist film formed on a semiconductor substrate is exposed to light, in order to form a pattern of the photoresist on the semi-conductor substrate (that is, a semiconductor wafer). At the time of the exposure, the light energy is absorbed into the photoresist film in a certain distribution in the depth direction of the photoresist film. In this manner, a standing wave which corresponds to the wavelength of the light during the exposure is created in the resist film.
Due to the occurrence of the standing wave during the exposure, an irregularity (of recesses and projections) that resembles the shape of the standing wave is created on the side wall of the resist pattern obtained developing the exposed resist.
When the shape of a standing wave is created on the side wall of a resist pattern as described above, some problems may occur. For example, measurements of the pattern of the underlying layer that is etched using a resist pattern as a mask may vary from one another. In order to avoid such problems, the side wall of the resist pattern should be made as smooth as possible. Accordingly, the occurrence of a standing wave within a resist film, as described above, should be inhibited or at least suppressed. This can be achieved by optimizing the thickness of the resist film and the structure and thickness of the film underlying the resist in advance by simulation.
In the meantime, in order to accurately observe the state of occurrence of a standing wave within a resist film by simulation, it is necessary to obtain a number of resist parameters with high accuracy, such as the type of the resist, the dissolving speed of the resist, the diffusion length of the acid depending upon the temperature of the post exposure bake (PEB), etc.
However, it is very difficult to obtain all these parameters accurately, and further, with the conventional simulation technique, there has been no methods of quantitatively determining the shape of a resist after calculating the resist shape. Therefore it has not been possible to optimize the parameters such as the thickness of the resist film and the structure and thickness of the film underlying the resist.
As described above, the conventional method of forming a resist pattern entails such a problem that the occurrence of a standing wave within a resist film cannot be avoided, i.e., the conditions such as the thickness of the resist film and the structure and thickness of the film underlying the resist film cannot be optimized in advance by simulation.